The present invention relates to a flip-chip packaged SMD-type (surface-mount device) light emitting diode, especially to a light emitting diode having an electrostatic protection device with function of standing electrostatic discharge (ESD) and without the need of wire bonding.
Light emitting diode (LED) is a fine solid-state light source made of semiconductor material. The device that turns electricity into light features on the compact structure, long lifetime, low driving voltage, fast response, and good shock resistance. It can also be applied in various appliances with light weight and compact design and is quite popular in our daily lives.
According to wavelength, LED is divided into visible LED and invisible LED. The visible LED is used for display. Moreover, the general LED and high brightness LED are differentiated by the brightness—one candle. The former is applied to indoor display systems while the later is suitable for outdoor display such as center high-mounted stop lamp, outdoor LED display and traffic signs. And the invisible light such as infrared LED is applied to sensor for defecting the size of copy paper, remote control of home appliances, auto-detection in plants, automatic doors and auto flush controllers.
During mass production of LED devices, the production of LED are divided into the upper, middle, and the lower streams. The main products of the upper stream are single chips and epi-wafers. Single crystals are substrate for raw materials and most of them are binary III-V group compound semiconductor such as gallium arsenide (GaAs) or gallium phosphide (GaP). While the epi-wafers are multiple layers of single crystal films with various thickness growing on the single crystal substrate such as AlxGa1-xAs/GaAs, AlxGayIn1-x-yP/GaAs, and InxGa1-xN/GaN. The common techniques used include Liquid Phase Epitaxy (LPE) and Metal Organic Vapor Phase Epitaxy (MOVPE). During the middle stream, according to the demands for the device, the epitaxy wafer is etched and metallized, and then cut into individual chips. The techniques used include photomask etching, dry/wet etching, vacuum evaporation and dicing. The lower stream means the packaging process. The chips are attached on the leadframe and then are packaged to form lamps, digit displays, dot matrix LED or surface mount devices.
Refer to FIG. 1, a conventional surface-mount device LED is disclosed. The LED 1′ is composed of a LED chip 10′ is on top of an electrode 16′ over a circuit board 20′. The LED chip 10′ is electrically connected with the electrode 16′by a wire 12′.
As to the gallium nitride-based III-V group compound semiconductor device using the sapphire substrate, the p-type electrode and the n-type electrode needs to be configured on the same side of the device. Thus the upward light-emitting surface of the devices packaged by conventional methods is shielded by electrodes, and lead to a certain upward light loss. The so-called flip chip structure is reversing the device and set a reflecting layer with higher reflectance on top of the p-type electrode. Thus the light originally emitted from the top of the device can also be emitted from other surface such as the top of the sapphire substrate. Thus the light loss on the electrode is reduced so that more light is emitted, compared with the device made by traditional packaging method. On the other hand, inside the flip chip structure, the heat dissipation structure of the package structure contacts the electrodes or bumps directly, the heat dissipation efficiency of the device is dramatically improved so as to avoid destruction of the device caused by heat.
Refer to FIG. 2, a schematic diagram of a prior art of conventional LED flip-chip products is disclosed. The device is composed of a LED chip 10′, placed on a base 30′. The LED chip 10′ having a substrate 110′, a first conductivity type semiconductor layer 120′, a second conductivity type semiconductor layer 130′, a first electrode 122′ formed on a confining area of the first conductivity type semiconductor layer 120′, a second electrode 132′ formed on a confining area of the second conductivity type semiconductor layer 130′. Two metal solders 40′ are arranged between a first lead frame 32′ and the first electrode 122′, a second lead frame 34′ the second electrode 132′ respectively.
Furthermore, a package structure of LED with protection device is disclosed in Taiwanese application No. 091103964, dated Jul. 5, 2002. Refer to FIG. 3, a structure of conventional lead-type LED flip chip products is shown. The device comprises a LED chip 10′ connected with an electrical and heat conductive pad 50′ by a solder 40′ while the electrical and heat conductive pad 50′ is attached on an electrical and heat conductive base substrate 60′. The n-type electrode of the LED chip 10′ connects with an electrostatic protection device 70′ by a solder 50′. The LED chip 10′ further includes an electrically conductive substrate 110′. By a wire 80′, the LED chip 10′ is connected with a second lead frame 92′ while the electrical and heat conductive base substrate 60′ is connected with a first lead frame 94′.
A conventional SMD (surface-mount device)-type LED with an electrostatic protection device is disclosed in FIG. 3A. The LED chip 10′ is connected with the electrostatic protection device 70′ by a solder 50′ while the electrostatic protection device 70′ is further connected with the first lead frame 94′ by the wire 80′. The above embodiment has the following disadvantages:
1. A stress appears during the wire bonding process of the device and causes the deformation or destruction of the devices so that the yield rate is reduced.
2. After wire bonding, a packaging process is performed. After the packaging, the wire always falls off. Thus this also causes the reduction of the yield rate.
3. Due to the need of wire bonding, the thickness of the light-emitting device can't be dramatically reduced.
Therefore, there is a need for improving the conventional flip-chip packaged light emitting diode. A flip-chip packaged SMD-type LED with antistatic function and having no wire bonding is provided to improve the above defects of wire bonding and also reduce the package area.